This invention relates to printing generally, and more specifically, to a reactive dye which may be thermally printed from a substrate, and a method of printing the reactive dye.
Words and designs are frequently printed onto clothing and other textile materials, as well as other objects. Common means of applying such designs to objects include the use of silk screens, and mechanically bonded thermal transfers. The silk screen process is well known in the art, and an example of a mechanical thermal bonding process to textile materials is described in Hare, U.S. Pat. No. 4,224,358.
The use of digital computer technology allows a virtually instantaneous printing of images. For example, video cameras or scanning may be used to capture an image to a computer. The image may then be printed by a computer driven printer, including thermal, ink jet, and laser printers. Computer driven printers are readily available which will print in multiple colors.
Heat activated, or sublimation, transfer dye solids change to a gas at about 400xc2x0 F., and have a high affinity for polyester at the activation temperature. Once the gassification bonding takes place, the ink is permanently printed and highly resistant to change or fading caused by laundry products. While sublimation dyes yield excellent results when a polyester substrate is used, these dyes have a limited affinity for other materials, such as natural fabrics like cotton and wool. Accordingly, images produced by heat activated inks comprising sublimation dyes which are transferred onto textile materials having a cotton component do not yield the high quality images experienced when images formed by such inks are printed onto a polyester substrate. Images which are printed using sublimation dyes applied by heat and pressure onto substrates of cotton or cotton and polyester blends yield relatively poor results.
The natural tendency of the cotton fiber to absorb inks causes the image to lose its resolution and become distorted. Liquid inks other than sublimation inks wick, or are absorbed by cotton or other absorbent substrates, resulting in printed designs of inferior visual quality, since the printed colors are not properly registered on the substrate. To improve the quality of images transferred onto substrates having a cotton component or other absorbent component, substrates are surface coated with materials such as the coatings described in DeVries, et. al., U.S. Pat. No. 4,021,591. Application of polymer surface coating materials to the substrate allows the surface coating material to bond the ink layer to the substrate, reducing the absorbency of the ink by the cotton and improving the image quality.
Gross coverage of the substrate with the surface coating material does not match the coating with the image to be printed upon it. The surface coating material is applied to the substrate over the general area to which the image layer formed by the inks is to be applied, such as by spraying the material, or applying the material with heat and pressure from manufactured transfer sheets, which are usually rectangular in shape. To achieve full coverage of the surface coating, the area coated with the surface coating material is larger than the area covered by the ink layer. The surface coating extends from the margins of the image after the image is applied to the substrate, which can be seen with the naked eye. The excess surface coating reduces the aesthetic quality of the printed image on the substrate. Further, the surface coating tends to turn yellow with age, which is undesirable on white and other light colored substrates. Yellowing is accelerated with laundering and other exposure to heat, chemicals, or sunlight. A method described in Hale, et. al., U.S. Pat. No. 5,575,877, involves printing the polymer surface coating material to eliminate the margins experienced when aerosol sprays or similar methods are used for gross application of the polymeric coating material.
A process of thermal transfers wherein the ink mechanically bonds to the substrate is described in Hare, U.S. Pat. No. 4,773,953. The resulting mechanical image, as transferred, is a surface bonded image with a raised, plastic like feel to the touch. Thermal transfer paper can transfer an image to a final substrate such as cotton, however, this method has several limitations. First, the entire sheet is transferred, not just the image. Second, such papers are heavily coated with polymeric material to bind the image onto the textile. This material makes the transfer area very stiff and has poor dimensional stability when stretched. Finally, the laundering durability is not improved to acceptable levels. The thermal transfer paper technology (cited Hare patent) only creates a temporary bond between the transfer materials and the final substrate. This bond is not durable to washing.
The use of reactive dyes for printing on cotton and other natural fibers is well known in the art. For example, Gutjahr, et. al. in xe2x80x9cTextile Printingxe2x80x9d, Second Edition, pp. 157-163 and Akerblom, et. al., U.S. Pat. No. 5,196,030 describe methods for the use of reactive dyes in print pastes for direct printing onto cellulosic fabrics using traditional printing techniques, such as silk-screen printing. Mehl, et. al, U.S. Pat. No. 4,664,670 describes the use of a transfer sheet impregnated with a nitrogen-containing compound that is printed by offset, gravure, or other traditional techniques using a sparingly soluble, non-subliming dye and a binder. The image thus produced is then transferred to cellulose or polyamide fibers. Koller, et. al., U.S. Pat. No. 4,097,229 describes the use of anthraquinone-type, sublimable, fiber-reactive disperse dyes that can be applied to a carrier sheet by spraying, coating, or printing, by such methods as flexogravure, silk-screen, or relief printing, and subsequently heat transferred to cellulose or polyamide fabrics. None of these processes are printed digitally and require pre- and after-treatments.
Digital printing processes using reactive dyes are known. For example, Yamamoto, et. al, U.S. Pat. No. 5,250,121 describes the use of a monochlorotriazine and /or vinyl sulfone reactive dye in an aqueous ink jet ink for printing directly onto pretreated cellulosic fabric. Von der Eltz, et. al., U.S. Pat. No. 5,542,972 describes the use of an aqueous formulation including a reactive dye whose reactive group contains a cyanamido group and an alkaline agent. The inks are used to print onto paper as a final substrate.
Melt transfer printing has been used since the nineteenth century to transfer embroidery designs to fabric. A design is printed on paper using a waxy ink, then transferred with heat and pressure to a final substrate. The Star process, developed by Star Stampa Artistici di Milano, uses a paper that is coated with waxes and dispersing agents. The design is printed onto the coated paper by gravure printing using an oil and wax based ink. The print is then transferred to fabric by pressing the composite between heated calendar rollers at high pressure. The ink melts onto the final substrate carrying the coloring materials with it. Fabrics printed in such a method using direct dyes are then nip-padded with a salt solution and steamed. Vat dyes can also be used in the ink, but the fabric must be impregnated with sodium hydroxide and hydros solution and steamed. The residual waxes from the transfer ink are removed during washing of the fabric.
Thermal wax transfer printing utilizes a transfer ribbon consisting of a hot-melt ink coated onto a film such as PET, or Mylar. The imaging process consists of passing the ribbon past the thermal heads of a printer to cause the hot-melt ink to transfer from the ribbon to a receiver sheet. Typically, the colorants used are pigments and the receiver sheet is plain paper or a transparency. Another form of thermal transfer printing known as dye diffusion thermal transfer, or D2T2, is similar to thermal wax transfer printing. In D2T2 the colorants are dyes of the disperse or solvent type rather than pigments, and the receiver sheet is usually white plastic. Niwa, et. al., G.B. Patent No. 2,159,971A makes use of reactive disperse sublimation dyes for D2T2 printing. The dye, once transferred, forms a covalent bond with a modified receiver sheet, containing free hydroxy or amino groups. The dye, thus anchored to the receiver sheet gives good fastness properties to solvents and heat.
This invention is a formulation and method of printing an ink or meltable ink layer which comprises reactive dyes or mixtures of reactive dyes and disperse dyes as colorants. The ink or ink melt layer also includes an alkaline substance, an optional heat-activated printing additive, such as urea, and a binder material, such as wax. Permanently bonded color images are provided by the reaction between the reactive dye and the final substrate, which may be any cellulosic, protein, or polyamide fiber material, or mixtures with polyester, but not until heat activation of the printed ink image.
A digital printer prints an image onto an intermediate medium, which may be paper, at a relatively low temperature, so that the ink is not activated during the process of printing onto the medium. The image formed by the printed ink is transferred from the intermediate medium to a final substrate on which the image is to permanently appear, such as by the application of heat and pressure which activates the ink. The process produces an image on the final substrate which is water-fast and color-fast.
To prevent premature or undesired reaction, the reactive dye is protected by the wax or wax-like binder material. The protecting properties of the wax material are removed by the application of energy or heat at a temperature which is above the temperature at which printing onto the intermediate medium occurs, and which is above the melting point of the wax. This higher temperature is presented during the transfer step, or the activation step, of the process, activating the ink which has been printed in an image onto the final substrate. The colorant is thereby permanently covalently bonded to the final substrate in the form of the desired printed image.
Alternatively, a digital printer prints an image onto a substrate, followed by application of sufficient heat and pressure which activates, or fixes the ink and permanently bonds the image to the final substrate.